Internal combustion engines convert chemical energy from a fuel into mechanical energy. Most internal combustion engines inject an air-fuel mixture into one or more cylinders. The fuel ignites to generate rapidly expanding gases that actuate a piston in the cylinder. The fuel can be ignited by compression such as in a diesel engine or through some type of spark such as the spark plug in a gasoline engine. The piston usually is connected to a crankshaft or similar device for converting the reciprocating motion of the piston into rotational motion.
Many internal combustion engines have a turbocharger to pressurize or boost the amount of air flowing into the cylinders. The additional air in a cylinder permits the combustion of additional fuel in the cylinder. The combustion of additional fuel increases the power generated by the engine.
Turbochargers typically operate in response to the engine operation. Generally, a turbocharger spins faster when the engine speed is increased and spins slower when the engine speed decreases. If the turbocharger operates too fast, the turbocharger output can reduce engine performance and can damage the turbocharger and other engine components. If the turbocharger operates too slow, the engine can hesitate, loose power, or otherwise operate inefficiently. Thus, there is an operating range for optimal turbocharger performance.
Most turbocharged diesel engines have an air supply system that, as engine speed and load is increased, the turbocharger rotations per minute (RPM) increases, causing the air flow and the pressure to the engine to increase. This results in changes to the in-cylinder trapped air density, and turbulence and swirl, which makes optimization of the combustion system difficult. The turbocharger efficiency also can be affected by changes in atmospheric pressure, ambient temperature, and engine speed.
In an ideal, optimized combustion system using a turbocharger, a constant flow velocity and a constant in-cylinder air density would be produced independent of engine speed and load, and therefore the fuel injection system could produce the same injection profile independent of engine speed and load. With these features, the combustion system could be optimized independent of engine speed and load. Thus, supplying air at a constant pressure independent of engine speed, in a manner that is practical, low-cost and easily implemented on a traditional turbocharger, is needed.